Respiratory diseases represent an increasingly important category of illness. The incidence of such diseases is expected to steadily increase with world industrialization and the rise of atmospheric pollutants. Among respiratory diseases of concern is chronic bronchitis.
In man, the lower conductive airway system begins with the trachea which divides into a series of inverted "Y" air conducting passages. The parts of the system of lower conducting airways in man comprise the two stem bronchi, the smaller bronchi, and the bronchioles. If the trachea is regarded as the starting branch, then the bronchi represent 1 to 3 stage branching and the bronchioles are 4 to 16 stage branching. These airway branches are the site of chronic bronchitis.
Chronic bronchitis is a condition associated with excessive tracheobronchial mucus production sufficient to cause cough with expectoration. The primary structures that experience anatomical change in chronic bronchitis are the conductive airways. Bronchial walls become narrowed by vasodilation, congestion, and mucosal edema. Moreover, chronic bronchitis is associated with hyperplasia and hypertrophy of the mucus-producing glands. Patients with predominant bronchitis are often overweight and cyanotic with a history of cough and sputum production.
Cigarette smoking is highly correlated with chronic bronchitis. The excessive mucus production and chromic cough are prominent symptoms of chronic bronchitis often called, "smoker's cough." Inflammation around the small airways is known as respiratory bronchiolitis and is usually one of the earliest changes that occurs in the lungs of cigarette smokers.
Chronic bronchitis is readily distinguished from bronchial asthma. With asthma the smooth muscle tissue in the walls of the bronchi and bronchioles contracts, causing airway obstruction and an increase in airway resistance. Asthma is an episodic disease. During an asthma attack, the smooth muscles surrounding the small airways of the lungs constrict in response to a particular stimulus. The symptoms of asthma often consist of dyspnea, cough, and wheezing.
A great need remains to develop new methods of treating chronic bronchitis by the use of improved therapeutic agents.